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Full text of "The manufacture and properties of iron and steel"

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6                                                   INTRODUCTION.
Wronght-iron is made by melting pig-iron in contact with iron ore and burning out the silicon, carbon and phosphorus, leaving metallic iron. This iron is not in a melted state when finished, for the temperature of the furnace is not sufficiently high to keep it fluid after the carbon has burned. It is in a pasty condition and is mixed with slag and when taken out of the furnace is a honeycomb of iron, with each cell full of melted lava, and this honeycomb is squeezed and rolled until most of the slag is worked out and the iron framework is welded together into a compact mass. The bars are rough and full of flaws and are regarded as an intermediate product. This "muck bar" is then cut up and "piled" and heated to a welding heat and rolled again, and this time the bar is clean and becomes the "merchant iron" of commerce.
The previous description refers to the use of pig-iron only, but in many works this practice is modified by using scrap of various kinds, especially steel turnings from machine shops. Oftentimes almost the entire charge is made of cast-iron borings and steel turnings, although a certain amount of larger steel scrap is generally used to make the ball hold together. In making the pile for the second rolling a certain proportion of soft steel scrap is often used, as this welds up with the rest, so as to be practically the same, and this increases- the tensile strength of the bar. The main principles of the process; however, remain the same in all its forms.
In the olden time all kinds of steel, whether made in the crucible, in the cementation chamber, or in the puddle furnace, contained carbon enough to make them suitable for. cutting tools when hardened in water, and the steels that were made in the Bessemer converter during the early days of its history were all more or less hard, much of it being used for tools; consequently the metal made in the converter was rightly called Bessemer steel.
As time went on and the cost of the operation was reduced below that of making wrought-iron, a great deal of very soft metal was made in the converter and in the open-hearth furnace. This new metal did not fill the old definition of steel, but it was impossible to draw any line between the steel used for rails and that used for forgings, and it was impossible'to draw a line between the metal used for forgings and that used for boiler plate, and as it was impossible to do this, practical men in America and England did